Welding material for heat-resistant steel

Abstract

Welding material for heat-resistant steel, the welding material comprising a flux and a sheath surrounding the flux, wherein the welding material contains, in wt.%, carbon (C): 0.03% to 0.3%, manganese (Mn): 0.5% to 3.0%, silicon (Si): 0.1% to 2.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, nickel (Ni): 20% to 40%, chromium (Cr): 15% to 35%, molybdenum (Mo): 2.0% or less, TiO2: 3% to 7%, SiO2: 0.5% to 2.5%, ZrO2: 0.5% to 2.5% and a balance of Fe and unavoidable impurities, wherein the flux contains, in wt.%, carbon (C): 0.1% to 2.0%, manganese (Mn): 2.0% to 10.0%, silicon (Si): 0.5% to 8.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, chromium (Cr): 40% to 80%, molybdenum (Mo): 0.1% to 8.0%, TiO2: 7% to 25%, SiO2: 2% to 10%, ZrO2: 1% to 10% and a balance of iron (Fe) and unavoidable impurities, and wherein the shell comprises a Ni-Fe-based alloy having a nickel content of 30% to 50%.

Description

Technical area

[0001] The present invention relates to a welding material and more particularly to a welding material for heat-resistant steels for high-temperature applications. State of the art

[0002] Heat-resistant steels used for high-temperature applications such as nuclear reactors, power plant pipes, blast furnaces, fluidized-bed furnaces, or annealing furnaces must have high-temperature strength and crack resistance. Such heat-resistant steels can be used to manufacture structures through welding processes, and the welded areas of such structures must also have high-temperature strength and crack resistance. Examples of welding materials for heat-resistant steel are disclosed in JP 2003-136280 A and JP H07-116891 A.

[0003] For example, austenitic stainless steels or Ni- or Co-based ultra-heat-resistant alloys have been used as heat-resistant steels. However, both steel sheets and welding materials based on Ni- or Co-based ultra-heat-resistant alloys are expensive due to the high contents of relatively expensive alloying elements. Since gas tungsten arc welding (GTAW) is used, wettability and productivity are poor. Therefore, the application of Ni- or Co-based ultra-heat-resistant alloys is very limited. On the other hand, austenitic stainless steels can be machined by any type of welding with a high degree of productivity, such as flux-cored arc welding (FCAW), taking economic aspects and weldability into account. Furthermore, austenitic stainless steels are relatively inexpensive.Thus, the use of austenitic stainless steels has increased since the 1980s.

[0004] In particular, among the austenitic stainless steels (STS 300 series steels), fully austenitic stainless steels with relatively high degrees of high-temperature resistance, high-temperature strength, and ductility were primarily used for applications in high-temperature, highly corrosive environments such as nuclear reactors, power plant piping, blast furnaces, fluidized-bed furnaces, or annealing furnaces. Fully austenitic stainless welding materials (STS 310 series welding materials) were used for such fully austenitic stainless steels.

[0005] However, cracks are easily formed in the welded areas of STS 310 series welding materials. Like the base materials, STS 310 series welding materials, which have a fully austenitic solidification structure formed by single-phase strengthening, have high nickel (Ni) and chromium (Cr) contents and a high degree of thermal expansion. However, it is known that because the solubility of phosphorus (P) and sulfur (S) is high in welded areas formed using STS 310 series welding materials, δ-ferrite, which effectively reduces high-temperature cracking, does not form in the welded areas. And because the welded areas undergo single-phase strengthening, high-temperature cracking is easily generated.

[0006] In a welding process using an austenitic weld metal, phosphorus (P) or sulfur (S) forms a low-melting-point eutectic compound, such as Fe3P or FeS, which separates along grain boundaries and exists in a liquid state during solidification, promoting high-temperature cracking. The phosphorus (P) and sulfur (S) content in currently commercially available STS 310 series weld metals is high, ranging from approximately 200 ppm to 300 ppm, due to the manufacturing processes and compositional characteristics of the STS 310 series weld metals.STS 310 series welding materials, which are widely used for STS 300 series heat-resistant steels, which are typical heat-resistant materials, are fully austenitic materials without δ-ferrite, and during a welding process using such STS 310 series welding material, phosphorus (P) and sulfur (S) contained in the base metal and weld metal separate along grain boundaries of the weld material, causing cracks.

[0007] To address these problems, a flux-cored welding material (Patent Document 1) was proposed, which includes a shell made of an STS 300 series steel, such as STS 304L or 316L, and a flux contained within the shell. Specifically, with reference to Patent Document 1, the shell is made of an STS 300 series stainless steel, and components such as a rare earth element (REM) or calcium (Ca) are added to the flux to inhibit cracking caused by phosphorus (P) and sulfur (S). However, the welding material disclosed in Patent Document 1 also has high contents of phosphorus (P) and sulfur (S), and thus, cracking in a welded portion cannot be completely prevented.

[0008] Therefore, it is necessary to develop a welding material that is capable of preventing the formation of cracks in a welded area of ​​heat-resistant steel.

[0009] (Patent Document 1) Korean Patent KR 10-1118904 RevelationTechnical Problem

[0010] An aspect of the present disclosure may provide a welding material capable of inhibiting the formation of cracks in a welding area of ​​heat-resistant steel. Technical solution

[0011] According to one aspect of the present disclosure, a welding material for heat-resistant steel is provided having the features of claim 1. The welding material for heat-resistant steel comprises a flux and a shell surrounding the flux, wherein the welding material contains, in wt.%, carbon (C): 0.03% to 0.3%, manganese (Mn): 0.5% to 3.0%, silicon (Si): 0.1% to 2.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, nickel (Ni): 20% to 40%, chromium (Cr): 15% to 35%, molybdenum (Mo): 2.0% or less, TiO2: 3% to 7%, SiO2: 0.5% to 2.5%, ZrO2: 0.5% to 2.5% and a balance of Fe and unavoidable impurities, wherein the flux contains, in wt%, carbon (C): 0.1% to 2.0%, manganese (Mn): 2.0% to 10.0%, silicon (Si): 0.5% to 8.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, chromium (Cr): 40% to 80%, molybdenum (Mo): 0.1% to 8.0%, TiO2: 7% to 25%, SiO2: 2% to 10%, ZrO2: 1% to 10%, and a balance of iron (Fe) and unavoidable impurities, and wherein the shell comprises a Ni-Fe-based alloy with a nickel content of 30% to 50%.

[0012] Advantageous further developments of the invention emerge from the subclaims. Beneficial effects

[0013] The welding material of the present disclosure can prevent the formation of cracks in the welded areas of heat-resistant steels for high-temperature applications such as blast furnaces, fluidized-bed furnaces, nuclear reactors, or power plants. Therefore, the welding material can be safely used in various applications.

[0014] Furthermore, since weld areas formed using the welding material of the present disclosure have a fully austenitic microstructure with a high degree of low-temperature toughness, the welding material can be used to form crack-free weld areas for liquefied natural gas (LNG) tanks with cryogenic properties. That is, the welding material of the present disclosure can also be used to manufacture structures from thick austenitic steel sheets in various fields such as oil refining, piping systems, construction, shipbuilding, or marine engineering. Preferred embodiment

[0015] A welding material is described in detail below. The present invention is not limited to the embodiments. According to an exemplary embodiment of the present invention, the welding material is a flux-cored welding material comprising a flux and a shell surrounding the flux.

[0016] The welding material of the exemplary embodiment contains carbon (C): 0.03% to 0.3%, manganese (Mn): 0.5% to 3.0%, silicon (Si): 0.1% to 2.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, nickel (Ni): 20% to 40%, chromium (Cr): 15% to 35%, molybdenum (Mo): 2.0% or less, TiO2: 3% to 7%, SiO2: 0.5% to 2.5% and ZrO2: 0.5% to 2.5% based on the total weight of the welding material including the flux and the shell.

[0017] Carbon (C) promotes austenite formation and improves strength. If the carbon (C) content is less than 0.03%, it is difficult to guarantee high-temperature strength. Conversely, if the carbon (C) content is more than 0.3%, excessive eutectic mixtures will form during welding, leading to high-temperature cracking and the generation of welding fumes and spatter. Therefore, it may be preferable for the carbon (C) content to be in the range of 0.03% to 0.3%.

[0018] During welding, manganese (Mn) reacts with oxygen (O) and sulfur (S), removing oxygen (O) and sulfur (S). Therefore, manganese (Mn) is added in an amount of 0.5% or more. However, if manganese (Mn) is added in an amount of more than 3%, the molten metal fluidity decreases, thereby reducing weld penetration and arc stability. Therefore, it may be preferable for the manganese (Mn) content to be in the range of 0.5% to 3.0%.

[0019] Preferably, silicon (Si) can be added in an amount of 0.1% or more to maximize deoxidation along with manganese during welding. However, if silicon (Si) is added in an amount greater than 2.0%, crack resistance decreases due to excessive formation of eutectic mixtures. Therefore, it may be preferable for the manganese (Mn) content to be in the range of 0.1% to 2.0%.

[0020] Even small amounts of phosphorus (P) and sulfur (S) promote the formation of low-melting-point compounds, thereby lowering the melting point of the weld metal and increasing its sensitivity to high-temperature cracking. Therefore, the phosphorus (P) and sulfur (S) contents should be kept as low as possible. Although phosphorus (P) and sulfur (S) are unavoidable, it is preferable that the phosphorus (P) and sulfur (S) contents be less than 0.01% each.

[0021] Nickel (Ni) is an austenite-forming element, preferably added in an amount of 20% or more to promote the formation of a fully austenitic structure and ensure resistance to high-temperature oxidation, high-temperature strength, and ductility. However, if the nickel (Ni) content exceeds 40%, the viscosity of a weld area increases excessively, causing the formation of pores and insufficient weld penetration. Therefore, the nickel (Ni) content is preferably set at 40% or less.

[0022] Although chromium (Cr) is a ferrite-forming element, it is preferable for the chromium (Cr) content to be 15% or more. However, if the chromium (Cr) content exceeds 35%, ductility decreases due to the formation of ferrite and chromium carbides at high temperatures. Therefore, it may be preferable for the chromium (Cr) content to be in the range of 15% to 35%.

[0023] Molybdenum (Mo) can be added to increase high-temperature strength and oxidation resistance. However, if the molybdenum (Mo) content exceeds 2.0%, ductility may decrease. Therefore, it may be preferable for the molybdenum (Mo) content to be in the range of 2.0% or less.

[0024] TiO2 stabilizes arcs and forms slag. If the TiO2 content is less than 3%, unstable arcs result. Slag forms particularly when TiO2 is present in too small amounts. In this case, a weld metal may not be completely covered with slag, resulting in rough weld beads. However, if the TiO2 content exceeds 7%, the addition of alloying elements to the interior of a cladding strip is limited, and excessive slag may be formed. Therefore, it may be preferable for the TiO2 content to be in the range of 3% to 7%.

[0025] SiO2 increases slag viscosity. If the SiO2 content is less than 0.5%, the viscosity-increasing effect is insufficient, and if the SiO2 content is more than 2.5%, the viscosity-increasing effect is excessive, causing defects such as residual inclusions. Therefore, it may be preferable for the SiO2 content to be in the range of 0.5% to 2.5%.

[0026] ZrO2 has a high melting point and thus increases the slag melting point. Therefore, it may be preferable for the ZrO2 content to be in the range of 0.5% or more. However, if the ZrO2 content is more than 2.5%, unfused sparks will form around an arc. Therefore, it may be preferable for the ZrO2 content to be in the range of 0.5% to 2.5%.

[0027] Preferably, the total content of phosphorus (P) and sulfur (S) in the weld material can be set to 0.012% or less. Since the crack sensitivity of a weld area during solidification increases as the total contents of phosphorus (P) and sulfur (S) increase, it is preferable to lower the total content of phosphorus (P) and sulfur (S). That is, when considering the composition of a base metal and the mixture of the base metal and weld material, it may be preferable that the total content of phosphorus (P) and sulfur (S) is in the range of 0.012% or less.

[0028] In addition, the welding material of the exemplary embodiment may further contain at least one element selected from the group consisting of copper (Cu): 1.0% or less, aluminum (Al): 0.5% or less, and magnesium (Mg): 0.5% or less.

[0029] Copper (Cu) may be added in an amount of 1.0% or less to improve oxidation resistance.

[0030] Aluminum (Al) and magnesium (Mg) can be added to a weld metal for deoxidation, desulfurization, and microstructure refinement. However, if the respective aluminum (Al) and magnesium (Mg) contents exceed 0.5%, the surface tension of the weld metal may increase, resulting in excessive spatter. Therefore, it may be preferable for the aluminum (Al) and magnesium (Mg) contents to be in the range of 0.5% or less each.

[0031] In addition, the welding material of the exemplary embodiment may further contain at least one element selected from the group consisting of titanium (Ti): 0.5% or less, fluorine (F): 0.5% or less, Na2O: 0.25% or less, K2O: 0.3% or less, Al2O3: 0.5% or less, MnO: 0.5% or less, and MgO: 0.5% or less.

[0032] Titanium (Ti) can be added to ensure arc stability and prevent intergranular corrosion. However, if the titanium (Ti) content exceeds 0.5%, carbides or nitrides will form in a weld area, and ductility may decrease. Therefore, it may be preferable to have a titanium (Ti) content in the range of 0.5% or less.

[0033] Fluorine (F) can be added to improve weld slag dispersibility. However, if fluorine (F) is added in excess of 0.5%, the slag viscosity may be too low, thus deteriorating the shape of weld beads. Therefore, it may be preferable to keep the fluorine (F) content in the range of 0.5% or less.

[0034] Na2O and K2O are alkali oxides that are highly prone to ionization and have the effect of improving slag flowability. However, if the Na2O content exceeds 0.25% and the K2O content exceeds 0.3%, excessive welding fumes can be generated.

[0035] Al2O3, MnO, and MgO can be added to control slag viscosity, thus promoting the formation of high-quality weld beads and protecting the weld pool. However, it may be preferable for the contents of Al2O3, MnO, and MgO to be in the range of 0.5% or less each.

[0036] The following describes in detail the shell of the welding material of the exemplary embodiment.

[0037] Preferably, the shell may be formed from a Ni-Fe-based alloy containing nickel (Ni) in an amount of 30% to 50%. According to the exemplary embodiment, in order to provide a welding material for a high-alloy stainless steel with high corrosion resistance, high-temperature corrosion resistance, high-temperature strength, high ductility, and high-temperature crack resistance, the shell may be formed from a high-alloy shell material such as a Ni-Fe-based alloy with very low contents of phosphorus (P) and sulfur (S) and a high content of nickel (Ni), which is a heat-resistant alloying element.

[0038] Because the shell has a high nickel content, the chromium (Cr) content can be reduced to lower the solubility of phosphorus (P) in the shell, thus minimizing the phosphorus (P) content in the weld zone. Furthermore, because the shell does not contain factors such as chromium compounds that promote precipitation hardening, the shell can exhibit high degrees of formability, ductility, and machinability. This means that a high-nickel weld material for heat-resistant steel can be provided.

[0039] In the exemplary embodiment, the Ni-Fe-based alloy may be a 36% Invar alloy.

[0040] The flux of the welding material of the exemplary embodiment will be described in detail below.

[0041] The flux contains carbon (C): 0.1% to 2.0%, manganese (Mn): 2.0% to 10.0%, silicon (Si): 0.5% to 8.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, chromium (Cr): 40% to 80%, molybdenum (Mo): 0.1% to 8.0%, TiO2: 7% to 25%, SiO2: 2% to 10% and ZrO2: 1% to 10% based on the weight of the flux.

[0042] Carbon (C) is an element that stabilizes austenite and improves strength. If the carbon (C) content is less than 0.1%, high-temperature heat resistance cannot be guaranteed. Conversely, if the carbon (C) content is more than 2.0%, excessive fumes and spatter may be generated during welding. Therefore, it may be preferable for the carbon (C) content to be in the range of 0.1% to 2.0%.

[0043] During welding, manganese (Mn) reacts with oxygen (O) and sulfur (S), forming slag as a product of deoxidation and desulfurization reactions. As a result, the manganese (Mn) content decreases. For this reason, manganese (Mn) is added in an amount of 2.0% or more. However, if manganese (Mn) is added in an amount of more than 10%, fume generation increases and molten metal fluidity decreases significantly. Therefore, it may be preferable for the manganese (Mn) content to be in the range of 2.0% to 10.0%.

[0044] During welding, silicon (Si) acts together with manganese (Mn) as a deoxidizer and forms slag. Considering this, it may be preferable for the silicon (Si) content to be in the range of 0.5% or more. However, if the silicon (Si) content exceeds 8%, crack resistance decreases. Therefore, it is preferable for the silicon (Si) content to be 8% or less.

[0045] Phosphorus (P) and sulfur (S) are impurities in the flux, and the contents of phosphorus (P) and sulfur (S) are each controlled to be 0.01% or less based on the weight of the flux. However, if the contents of phosphorus (P) and sulfur (S) are each more than 0.01%, high-temperature crack sensitivity increases because the phosphorus (P) and sulfur (S) in the flux mix with the phosphorus (P) and sulfur (S) diffused from the shell and a base metal. Therefore, the contents of phosphorus (P) and sulfur (S) are preferably controlled to be 0.01% based on the weight of the flux.

[0046] Chromium (Cr) is an element added to stainless steels and welding materials to improve high-temperature corrosion resistance and high-temperature strength, and to stabilize austenite. When the shell of the exemplary embodiment is an Fe-Ni-based alloy shell, the chromium (Cr) content may preferably be 20% or more. However, if the chromium (Cr) content is more than 80%, it is difficult to add other basic components such as carbon (C), manganese (Mn), silicon (Si), and TiO2 to the flux, and thus a flux-cored wire for all-position welding cannot be provided. Therefore, the chromium (Cr) content is preferably set to 80% or less.

[0047] Molybdenum (Mo) is added in an amount of 0.1% or more to improve high-temperature strength and oxidation resistance. However, if the molybdenum (Mo) content exceeds 8.0%, ductility may decrease, and wire breakage may frequently occur due to excessive filler content when the welding material is manufactured in wire form. Therefore, it may be preferable for the molybdenum (Mo) content to be 8.0% or less.

[0048] TiO2 is added to the flux to ensure arc stability and slag formation. If the TiO2 content is less than 7%, arc stability is not guaranteed. In particular, slag may form in too small quantities, resulting in weld beads that are not completely covered with slag, resulting in rough surfaces. Conversely, if the TiO2 content is more than 25%, the addition of base alloying elements such as carbon (C), chromium (Cr), silicon (Si), and manganese (Mn) into the interior of a cladding strip is limited, and weldability may decrease due to excessive slag. Therefore, it may be preferable for the TiO2 content to be in the range of 25% or less.

[0049] SiO2 added to the flux increases slag viscosity. However, if the SiO2 content is less than 2%, SiO2 has an insignificant viscosity-enhancing effect on the weld metal containing TiO2 as the main slag component. Conversely, if the SiO2 content is more than 10%, slag viscosity may increase excessively, increasing defects such as residual inclusions and the potential for cracking due to the high silicon content in a metal deposit. Thus, it may be preferable for the SiO2 content to be in the range of 10% or less.

[0050] ZrO2 has a high melting point and thus increases the slag melting point when added to the flux. For this purpose, the ZrO2 content is preferably 1% or more. However, if the ZrO2 content exceeds 10%, unfused sparks will form around an arc. Therefore, it may be preferable to have an upper limit of 10% for the ZrO2 content.

[0051] In addition, the flux may further contain at least one element selected from the group consisting of nickel (Ni): 8% or less, copper (Cu): 8% or less, aluminum (Al): 3.5% or less, magnesium (Mg): 2.5% or less, titanium (Ti): 3% or less, and F: 8% or less.

[0052] Nickel (Ni) added to a heat-resistant alloy stabilizes austenite and improves high-temperature corrosion resistance, high-temperature strength, and ductility. Although nickel (Ni) is generally added to the shell formed from an Fe-Ni-based alloy, nickel (Ni) can also be added to the flux to further improve high-temperature corrosion resistance, high-temperature strength, and ductility. However, when considering the addition of other components, it may be preferable for the nickel (Ni) content to be 8% or less.

[0053] Although copper (Cu) can be added to improve high-temperature oxidation resistance and guarantee the solubility of carbon (C), the content of copper (Cu) can preferably be adjusted to 8% or less.

[0054] Aluminum (Al) and magnesium (Mg) can be added to a weld metal for deoxidation, desulfurization, and microstructure refinement. However, if the aluminum (Al) content exceeds 3.5% and the magnesium (Mg) content exceeds 2.5%, the surface tension of the weld metal increases, resulting in excessive spatter. Therefore, it may be preferable for the aluminum (Al) content to be 3.5% or less and the magnesium (Mg) content to be 2.5% or less.

[0055] Titanium (Ti) can be added to ensure arc stability and prevent intergranular corrosion. However, if titanium (Ti) is added in excess, carbides or nitrides will form in a weld zone, thus reducing ductility. Therefore, it may be preferable for the titanium (Ti) content to be in the range of 3.0% or less.

[0056] Fluorine (F) is added to the flux in various forms, such as CaF2 or AlF6, to improve weld slag dispersibility. However, if the fluorine (F) content in the flux exceeds 8.0%, slag flowability may increase excessively, making it difficult to perform a full-position welding process and deteriorating the shape of weld beads. Therefore, it may be preferable for the fluorine (F) content to be 2.0% or less.

[0057] In addition, the flux may further contain at least one element selected from the group consisting of Na2O: 2.5% or less, K2O: 4.0% or less, Al2O3: 4.0% or less, MnO: 4.0% or less, and MgO: 4.0% or less.

[0058] Na2O and K2O are added to the flux as alkali components, which readily undergo ionization and improve slag flowability. However, if the Na2O content exceeds 2.5% and the K2O content exceeds 4.0%, excessive welding fumes will be generated. Therefore, it is preferable to adjust the Na2O content to 2.5% or less, and the K2O content to 4.0% or less.

[0059] Al2O3 and MgO increase slag viscosity, and MnO decreases it. Therefore, these components are added to the flux to control slag viscosity, leading to the formation of high-quality beads and protecting the weld pool. Considering the low specific gravities of Al2O3, MnO, and MgO, it may be preferable for the respective contents of Al2O3, MnO, and MgO to be 4.0% or less.

[0060] Preferably, the flux may be present in an amount of 15% to 40%. The flux filling ratio can be determined according to the size of a filling space and the flux composition, which depend on the composition, thickness, and width of the shell. If the flux filling amount is less than 15%, the flux amount may be insufficient to provide the welding material as a flux-cored wire for all-position welding. Conversely, if the flux filling ratio is more than 40%, breakage may frequently occur due to a metal shell that is too thin during a drawing process of flux-cored wire manufacturing processes, and thus the manufacturing processes cannot be carried out normally. Therefore, it may be preferable for the flux filling ratio to be in the range of 15% to 40%. Method of carrying out the invention

[0061] Examples of the present disclosure are described in detail below. The following example is provided for illustrative purposes and is not intended to limit the scope of the present disclosure. Examples

[0062] Welding materials with the compositions shown in Tables 1 and 2 were prepared (in Tables 1 and 2, the content of each component is in wt%, and the remainder is iron (Fe) and unavoidable impurities). A welding process was performed on a base metal by a welding method shown in Table 3 using the welding materials. Afterward, cracks, bead coverage, and defects other than cracks were observed in weld areas, and the results are shown in Table 4.

[0063] After the welding process, the ceramic tape and slag were removed, and the surface was brushed. The formation of high-temperature cracks was determined by observing cracks in the initial layer beads using a penetration test (PT). During the high-temperature crack inspection, the welding process was completed, and then radiographic testing (RT) was performed to detect cracks and other defects. Table 1 Table 2 Nr. F TiO2 SiO2 Na2O K2O Al2O3 MnO MgO ZrO2 Covering RS1 0,14 6,6 0,65 0,2 0,1 0,01 0,02 0 0,5 304L RS2 0,2 4,55 1,4 0,3 0,2 0,05 0,4 0,05 0,05 304L RS3 0,18 4,76 1,12 0,3 0,2 0,05 0,4 0 0,05 304L CS1 0,18 0,94 0,12 0,08 0,01 0 0 0 0,05 304L CS2 0,3 5,2 0,2 0,24 0,01 0 0 0,04 1,2 304L CS3 0,08 3,9 0,15 0,08 0 0,02 0 0,01 0,55 304L CS4 0,05 1,1 0,2 0,05 0,05 0 0 0,5 0,6 304L CS5 0,05 1,25 3 0 0 0,05 0 0,01 0,6 304L CS6 0,05 1,1 1 0,05 0,05 0 0,05 0,5 0 316L CS7 0,05 3,2 0,8 0,05 0 0 0 0,01 0,75 316L CS8 0,05 1,5 0,8 0,05 0 0 0 0,01 3,5 316L IS1 0,24 5 0,26 0,12 0 0 0,1 0 1,05 35%Ni-Fe IS2 0,24 5,4 0,26 0,12 0 0 0,1 0 1,05 35%Ni-Fe CS9 0,24 5,1 0,26 0,12 0 0 0,1 0 1,05 35%Ni-Fe IS3 0,24 5,1 0,26 0,12 0 0 0,1 0 1,05 35%Ni-Fe CS10 0,24 5 0,26 0,12 0 0 0,1 0 1,05 35%Ni-Fe IS4 0,24 5 0,26 0,12 0 0 0,1 0 1,05 35%Ni-Fe CS11 0,24 1,2 0,26 0,12 0 0 0,1 0 1,05 42%Ni-Fe IS-5 0,24 3,6 0,26 0,12 0 0 0,1 0 1,05 42%Ni-Fe IS6 0,24 3,6 0,26 0,12 0 0 0,1 0 1,05 42%Ni-Fe RS: Sample from related prior art CS: Reference sample IS: sample according to the invention Table 3 Base metal Base metal size (mm) Chamfering c-dimension Welding position Test conditions (A / V) Welding processes protective gas Fastening Endtab STS3105 200L*150W*30t 45°One side 8mm FOLD 190 / 32 Autocarriage CO2 100% Screw tensioning devices used Table 4 Nr. Crack formation Caterpillar cover Defects other than cracks RS1 ◯ ◯ × RS2 ◯ ◯ × RS3 ◯ ◯ × CS1 ◯ × × CS2 ◯ ◯ × CS3 ◯ ◯ × CS4 ◯ × ◯ (inclusions) CS5 ◯ ◯ × CS6 ◯ ◯ × CS7 ◯ ◯ × CS8 ◯ × × IS1 × ◯ × IS2 × ◯ × CS9 ◯ ◯ × IS3 × ◯ × CS10 ◯ ◯ × IS4 × ◯ × CS11 × × ◯ (inclusions) IS-5 × ◯ × IS6 × ◯ × RS: Sample from related prior art CS: Comparison sample IS: sample according to the invention Cracking: ◯ occurred, × did not occur Caterpillar coverage: ◯ good, × bad Defects other than cracks: ◯ Defect, × no defect

[0064] As shown in Table 4, in the case of weld materials meeting the conditions of the present disclosure, no cracks or other defects were observed, and high-quality beads were formed. This means that the weld materials had a high degree of weldability.

[0065] However, in the case of the related art samples and Comparative Samples 1 to 8, which had shells made of conventional 300 series steels, cracks were observed in welded areas. In the case of Comparative Examples 9, 10, and 11, which had shells made of high Ni-Fe alloys but did not meet the composition proposed in the present disclosure, cracks were observed in welded areas, poor bead coverage, or other defects.

Claims

[1] Welding material for heat-resistant steel, the welding material comprising a flux and a sheath surrounding the flux, wherein the welding material contains, in wt.%, carbon (C): 0.03% to 0.3%, manganese (Mn): 0.5% to 3.0%, silicon (Si): 0.1% to 2.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, nickel (Ni): 20% to 40%, chromium (Cr): 15% to 35%, molybdenum (Mo): 2.0% or less, TiO2: 3% to 7%, SiO2: 0.5% to 2.5%, ZrO2: 0.5% to 2.5% and a balance of Fe and unavoidable impurities, wherein the flux contains, in wt.%, carbon (C): 0.1% to 2.0%, manganese (Mn): 2.0% to 10.0%, silicon (Si): 0.5% to 8.0%, phosphorus (P): 0.01% or less, sulfur (S): 0.01% or less, chromium (Cr): 40% to 80%, molybdenum (Mo): 0.1% to 8.0%, TiO2: 7% to 25%, SiO2: 2% to 10%, ZrO2: 1% to 10% and a balance of iron (Fe) and unavoidable impurities, and wherein the shell comprises a Ni-Fe-based alloy having a nickel content of 30% to 50%. [2] The welding material according to claim 1, wherein a total content of phosphorus (P) and sulfur (S) in the welding material is 0.012% or less. [3] The welding material according to claim 1, wherein the welding material further contains at least one element selected from the group consisting of copper (Cu): 1.0% or less, aluminum (Al): 0.5% or less, and magnesium (Mg): 0.5% or less. [4] The welding material according to claim 1, wherein the welding material further contains at least one element selected from the group consisting of titanium (Ti): 0.5% or less, fluorine (F): 0.5% or less, Na2O: 0.25% or less, K2O: 0.3% or less, Al2O3: 0.5% or less, MnO: 0.5% or less, and MgO: 0.5% or less. [5] Welding material according to claim 1, wherein the Ni-Fe-based alloy is an Invar alloy. [6] The welding material according to claim 1, wherein a total content of phosphorus (P) and sulfur (S) in the flux is 0.01% or less. [7] The welding material according to claim 1, wherein the flux further contains at least one element selected from the group consisting of nickel (Ni): 8% or less, copper (Cu): 8% or less, aluminum (Al): 3.5% or less, magnesium (Mg): 2.5% or less, titanium (Ti): 3% or less and fluorine (F): 8% or less, the welding material further containing: copper (Cu): 1.0% or less, aluminum (Al): 0.5% or less, magnesium (Mg): 0.5% or less, titanium (Ti): 0.5% or less and fluorine (F): 0.5% or less. [8] The welding material according to claim 1, wherein the flux further contains at least one element selected from the group consisting of Na2O: 2.5% or less, K2O: 4.0% or less, Al2O3: 4.0% or less, MnO: 4.0% or less, and MgO: 4.0% or less, the welding material further contains: Na2O: 0.25% or less, K2O: 0.3% or less, Al2O3: 0.5% or less, MnO: 0.5% or less, and MgO: 0.5% or less. [9] The welding material according to claim 1, wherein the filling ratio of the flux is 15% to 40%.